1. Field of the Invention
This invention relates to lapping systems for hard drive magnetic heads, and more particularly to row tools used in lapping systems.
2. Description of the Related Art
Magnetic heads (also called sliders) for hard drives read data from the media (platter/disk) by sensing changes in magnetic field strength emanating from magnetic grains in the media. A writer is also included in the head that generates a magnetic field orienting the grains based on whether a one or zero is stored. The data is stored magnetically by alternating magnetic fields created by the writer as the gap (space between the poles) of the electromagnetic element glides (or slides) over the surface of the disk. The data is stored on the disk in a circular pattern with data tracks spaced as close as ten millionths of an inch apart, with as many as one hundred thousand tracks per inch. The data is stored by the writer in a track as individual “bits” at as many as five hundred thousand bits per inch, or as close together as two millionths of an inch. The data can then be read back by the reader-part of the head which contains a “magneto-resistive” material between two shields, with the magneto-resistive material changing resistance based on the magnetic orientation of a magnetic field.
Magnetic heads go through a number of processes before being lapped (or polished) to obtain the proper magnetic performance. The magnetic heads are typically deposited in rows on a wafer using fabrication and deposition techniques similar to those developed in the semiconductor industry. The wafer is then sliced into individual rows or a block of several rows of magnetic heads that are then bonded onto a row tool for the lapping operation. The row tool is then mounted in a lapping system/machine that laps the row of magnetic heads. Depending on the size of the heads and the length of the rows, there may be from 30 to 80 heads that are lapped simultaneously.
This lapping procedure removes material from the lower surface of the row and is one of the final procedures in manufacturing the magnetic heads/sliders. Using conventional lapping processes and row tools there was little to no control over the lapping of individual heads or groups of heads. As a result, all heads in the row had to meet the end performance target at the same time. Often times, however, the individual heads exhibit different performance characteristics at the end of lapping, and some of the heads characteristics are outside the acceptable range. These unacceptable heads are typically discarded which leads to waste that can increase the overall cost of the acceptable heads.
More recently, row tools have been developed that have control points that are designed to influence the row on the row tool to allow the lapping process to define the primary shape of the row of sliders. This also allows some control over the primary surface finish, device dimensions (distance from reading and writing elements to machined surface), and the shape and condition of the exposed surfaces. See U.S. Pat. Nos. 5,607,340 and 5,620,356 to Lackey et al.
FIG. 1 shows a more recent row tool 10 having a row of sliders 12 bonded on its lapping surface 14 that provides limited control over the lapping of the magnetic heads. Tool 10 includes seven “nodes” 16, or control points, and a lapping surface 14 to which a row of magnetic heads 12 can be mounted. The nodes 16 allow the lapping machine to alter the lapping surface 14 and thereby control the shape of row 12 mounted on lapping surface 14. The lapping machine manipulates the nodes by applying bending force (positive or negative force) at each node 16, which essentially bends the lapping surface 14. This bending provides the control of the shape of the lapping surface 14 row during the lapping which in turn controls the shape of row 12.
One of the primary disadvantages of row tool 10 is that each of the rows can have between approximately and 80 magnetic heads so that each of the seven control nodes 16 bends the lapping surface 14 under several magnetic heads. Force interpolation is required at nodes 16 to “estimate” a best fit line between the heads on the row for which a discrete bending node is not available. This results in a less than optimum dimensional control for the population of heads on a row.
A relatively recent advancement in row tool technology has been the development of row tools with bending nodes along the entire row of heads. This increases the number of control nodes from the previously conventional seven, to forty-eight (48) or more. For a row with forty-eight heads, each head can have its own bending node; referred to as Single Slider Level Lapping Technology (SLLT). FIG. 2 shows one embodiment of a SLLT row tool 20 having forty-eight nodes 22, each of which has a top surface, with the node top surfaces together serving as lapping surface 24. A row 26 of heads is arranged on lapping surface 24, preferably with one of the heads in row 26 over a respective one of nodes 22. Applying the required bending force (positive or negative force) at each head location in row 26 results in much better control over dimensional features of the full population of devices on row 26.
The row tool 20, however, has a lapping surface that is interrupted along its length by the spaces between the bending nodes 22. FIG. 3 shows row 26 mounted to nodes 22 with a respective head 28 arranged over a respective one of nodes 22. During lapping, the pressure of the lapping surface can cause row 26 to flex into the space between nodes 22. After the pressure is removed, row 26 flexes back such that the resulting lapped row 26 can have bumps 30 or other imperfections on its lapped surface.
Another disadvantage is that the bonding surface of the row tool can be ductile. As a result, the bonding surface can be altered such that the slider dimensions and geometry are undesirably changed. This can easily happen during the lapping process without detection so that many defective sliders will be fabricated. These defective sliders may not be usable, which leads to waste and increases costs.